The present invention relates to a melamine molded foam having a reduced fragility by improving strength, a good workability, and an enough resistance to moist heat aging and to a process for producing the same. In addition, the invention relates to a wiper having a washing portion comprising the melamine molded foam and having an excellent durability. The melamine molded foam of the invention can be used for various uses requiring heat-insulating properties, sound attenuation or electrically insulating properties as well as for the wiper. In particular, it is useful for the uses which require heat resistance or resistance to moist heat aging as well as heat-insulating properties such as engine room of automobiles and electrical home appliances (e.g., an electric rice cooker, a hot water supply system, a quilt drier and an oven toaster), which require heat resistance or resistance to moist heat aging as well as lagging properties such as a warm water-supplying pipes from boilers, or which require heat resistance or resistance to moist heat aging as well as sound absorbing qualities such as a microwave oven.
A floor cloth has conventionally been used for wiping the dust off a table and, in the case of washing tableware or a bath tab, an urethane foam or a cellulose sponge has been used. In some cases, however, dirt can not sufficiently be removed even when a detergent is used. Or, when rubbed too strongly, the rubbed surface to be washed might be damaged or suffer reduction in luster. Thus, wipers comprising a melamine foam excellent in washing off dirt have been proposed and have been put into practice. However, the melamine foam involves the problem that, since it is fragile due to its insufficient strength, it comes off in a particulate form when rubbed against the surface to be washed and the particles damage the surface similarly with the urethane foam.
In spite of its excellent heat resistance and its thermally stable properties, the melamine foam is in some cases limited as to its use due to this fragility and generation of reject articles resulting from the fragility. Further, although the fragility may not cause a serious problem in the use of heat-insulating materials and lagging materials, those materials which are exposed to a moist heat atmosphere such as lagging materials for warm water-supplying pipes from boilers suffer reduction in strength, thus so-called resistance to moist heat aging being important. Additionally, Japanese Patent Laid-Open No. 26054/1995 discloses a melamine foam having decreased fragility, which, however, is still insufficient and, in addition, it is not investigated therein to improve resistance to moist heat aging. Further, Japanese Patent Laid-Open No. 152848/1981 discloses a process for producing a melamine/formaldehyde elastic foam having a low density by heating for removing water, etc., but refers to nothing as to heat compression.
The invention solves the problems with the conventional products described above, and an object of the invention is to provide a melamine molded foam having a reduced fragility by improving strength, a good workability, and an enough resistance to moist heat aging and a process for producing the same. In addition, the other object of the invention is to provide a wiper having a washing portion comprising the melamine molded foam, showing an excellent dirt-removing ability without damaging the surface to be washed, and having an excellent durability.
It was tried to heat-compress a melamine foam to thereby increase its strength for reducing its fragility. First, as is the same with urethane foams which can easily be heat-molded, the melamine foam was heat-compressed at about 160 to about 180xc2x0 C. However, the heat-compressed foam easily recovered to the thickness before the heat compression with time at room temperature, thus a compressed molded foam not being produced. Then, the molding was conducted at a temperature within a higher specific range generally not being employed in the field of heat molding a resin foam. This time, sufficient plastic deformation of the melamine foam was attained, and there was obtained a melamine molded foam having an improved strength and a reduced fragility.
The invention has been completed based on the finding.
The above objects of the invention have been achieved by a melamine molded foam, a process for producing a melamine molded foam and a wiper each having the constitution described below:
(1) A melamine molded foam, wherein melamine foam is in a state of being heat-compressed to cause plastic deformation;
(2) The melamine molded foam as described in (1), wherein the melamine foam is compressed to a thickness of {fraction (1/1.2)} to {fraction (1/12)};
(3) The melamine molded foam as described in (1) or (2), which shows a dimensional recovery ratio of 40% or less when allowed to stand at 23xc2x0 C. for 200 hours;
(4) The melamine molded foam as described in one of (1) to (3), which has an uneven area in at least part of the surface thereof;
(5) A process for producing a melamine molded foam, which comprises heat-compressing a melamine foam at 210 to 350xc2x0 C. for 3 minutes or longer to cause plastic deformation;
(6) A process for producing a melamine molded foam, which comprises heat-compressing a melamine foam at a temperature lower than the decomposition temperature of the melamine monomer constituting the melamine foam by 140xc2x0 C. or less for 3 minutes or longer to cause plastic deformation;
(7) The process for producing a melamine molded foam as described in (5) or (6), wherein the melamine foam is compressed to a thickness of {fraction (1/1.2)} to {fraction (1/12)};
(8) The process for producing a melamine molded foam as described in one of (5) to (7), wherein the heat-compression molding is conducted in a metal mold having an uneven area in at least part of the molding surface with the melamine foam in contact with the uneven area-containing molding surface;
(9) The process for producing a melamine molded foam as described in one of (5) to (7), wherein the heat-compression molding is conducted with the melamine foam in contact with the uneven area-containing surface of a molding attachment which has the at least partly uneven surface;
(10) A wiper having a washing portion comprising the melamine molded foam described in one of (1) to (4); and
(11) The wiper as described in (10), which has the above-described washing portion and a multi-layer structure.